pangox-compat: depends on pkg-config

Fixes #17736.
bochs: depends on pkg-config
gtkwave: depends on pkg-config
gwyddion: depends on pkg-config
lablgtk: depends on pkg-config
libglade: depends on pkg-config
mjpegtools: depends on pkg-config
mtr: depends on pkg-config
putty: depends on pkg-config
pygtk: depends on pkg-config
sylpheed: depends on pkg-config
gqview: depends on pkg-config
apt-dater: depends on pkg-config
cpansearch: depends on pkg-config
enchant: depends on pkg-config
gts: depends on pkg-config
json-glib: depends on pkg-config
ldapvi: depends on pkg-config
libqalculate: depends on pkg-config
libwpd: depends on pkg-config